Recently, potential neuroprotective-effects of nicotine have been shown, and meanwhile various neurodegenerative-models in animals and cultured cells suffering from excitotoxic injury, athrepsia, ischemia, injury, neuronal cell death induced by amyloid beta (Aβ) or neurodegeneration induced by protein aggregation have been proposed. In many cases where nicotine shows neuroprotective effects, it has been found that nicotinic acetylcholine receptors containing alpha7 subtype are activated. These findings suggest that nicotine is useful in providing neuroprotective effects, and indicate that receptors containing α7-subtype are directly related with the effects. These data suggest that α7 nicotinic acetylcholine receptor is typically a suitable molecular-target for neuroprotection. In other words, the neuroprotection may be accomplished by developing an active agonist/positive modulator (i.e. positive allosteric modulator: PAM) of the receptor. In fact, α7 nicotinic acetylcholine receptor agonist has already been identified, and is expected to provide a possible clue to the development of neuroprotective drugs. In addition, it has recently been reported that α7 nicotinic acetylcholine receptor is also involved in inflammation. Thus, the development of a novel modulator of the receptor is expected to lead to a novel treatment for nervous system diseases, psychiatric diseases and inflammatory diseases.
In the past, there were some disclosures about modulators of α7 nicotinic acetylcholine receptor (α7 nAChR), but the chemical structures thereof are different from that of the present compound (see, Patent Reference 1 and Patent Reference 2).